Method of hot pressing metals and refractories



A. G. KING Sept. 5, 1967 I METHOD OF HOT PRESSING METALS ANDREFRACTORIES Original Filed Oct. 25. 1963 4 Sheets-Sheet l but INVENTOR.AM AN 6. KING ATToE VEY Sept, 5, 1967 A. G. KING 3,340,270

METHOD OF HOT PRESSING METALS AND REFRACTORIES Original Filed Oct. 25,1963 4 Sheets-Sheet 2 INVENTOR.

MM I ALAN G. MA/Q Sept. 5, 1967 A. G. KING 3,340,270

METHOD OF HOT PBESSING METALS AND REFRACTORIES Original Fi led Oct. 23,1963 4 Sheets-Sheet 3 A TTOENE Y United States Patent 3,340,270ll/IETHOD OF HOT PRESSING METALS AND REFRACTORIES Alan G. King, WestBoylston, Mass., assignor to Norton Company, Worcester, Mass., :1corporation of Massachusetts Original application Oct. 23, 1963, Ser.No. 318,322, now Patent No. 3,303,533, dated Feb. 14, 1967. Divided andthis application Nov. 17, 1965, Ser. No. 535,617

4 Claims. (Cl. 264-297) ABSTRACT OF THE DISCLOSURE A method for hotpressing or molding materials in a refractory mold at relatively hightemperatures and high pressures such as are required for ceramicswherein filled molds are successively delivered into and out of a hotpressing zone and pressure applying means are made to operate againstall sides of the mold during performance of the hot pressing stepindependently of the mold and furnace structure.

This application is a division of SN. 318,322, filed Oct. 23, 1963, nowUS. Patent 3,303,533, granted Feb. 14, 1967.

This invention relates to hot molding of ceramic articles in a widevariety of sizes and shapes which objects may be formed of ceramic orrefractory or even powdered metal material.

The principal objects of the invention are to provide a semiautomatichot press molding method wherein the size and strength of the molds maybe reduced materially by employing lateral support for the molds duringpressing instead of relying upon the strength of the mold itself therebyto make possible the use of materials compatible with the products beingmolded; less expensive mold construction; smaller molds; and a smallerfurnace and associated apparatus for handling the molds. Other objectsare to provide apparatus which may be automated; takes up less space;requires the attendance of only one operator; requires approximately aquarter of the operating time of existing equipment and hence provides amaterial increase in yield; and which requires little maintenance.

The invention will now be described in greater detail with reference tothe accompanying drawings wherein:

FIG. 1 is a perspective view of the hot pressing apparatus showing afurnace, a supporting frame for the furnace and for pressure-applyingmeans and symmetrically arranged supports designed to permit alternateoperation of two furnaces with a single supporting frame;

FIG. 2 is an elevation of the apparatus, showing a roller-type track formoving the furnaces into and out of the supporting frames at oppositeends;

FIG. 3 is an end elevation;

FIG. 4 is a vertical, longitudinal section taken through the furnaceremoved from its supporting frame;

FIG. 5 is a transverse section of the furnace taken on the line 5-5 ofFIG. 4;

FIG. 6 is an end elevation of a mold assembly;

FIG. 7 is a side elevation of the mold assembly shown in FIG. 6;

FIG. 8 is an end elevation of another kind of mold assembly;

FIG. 9 is a side elevation of the mold assembly shown in FIG. 8; and

FIG. 10 is a diagrammatic view of the pressure-applying means and thecontrols for effecting their operation in the proper sequence.

The apparatus herein illustrated is for the purpose of hot pressing acompressible material in a mold without requiring that the mold itselfbe strong enough to withstand the lateral pressure developed against thesides of the mold by application of compacting pressure at the ends ofthe mold. Briefly, this is accomplished by sliding a mold assembly,consisting of an open-end mold box with plungers inserted in its openends, into a tunneltype furnace, with the open ends transverse to thedirection of movement, to a zone of high temperature, supporting thefour walls of the mold box against deflection transverse to the openends by means of pressure-applying rams, and applying pressure by otherpressureapplying rams through the open ends of the mold box to compactthe material therein.

Referring to the drawing (FIG. 1), the apparatus comprises a furnace 10,a rigid supporting frame 12 for the furnace, and pressure-applying meansin the form of fluid motors 14 arranged at the sides and ends of thefurnace. Piers 16 support the frame and piers 18 at the opposite end ofthe frame, in conjunction with the piers 16, support a roller-typeconveyor 19 (FIG. 2), on which two furnaces are adapted to be movedalternatively into and out of the frame 12.

The supporting frame 12 is comprised of intermediate and end members20-20 and 22-22 comprised of structural steel beams, the beams making upeach member being welded together at their corners by means of gussetplates 24. The intermediate members 20-20 are connected in spacedparallel relation by steel tubes 26 welded to the gusset plates and arereinforced against deflection under load by tie rods 28. The end members22-22 have steel tubes 30 welded to their gusset plates at their cornersand are held in spaced parallel relation to the intermediate members bytubes 32 extending through the tubes 26 and 30. The end members 2222 arefurther strengthened by detachable tie rods 50 at each of the corners. Aplate 33 is welded across the intermediate members 20-20 at each of thefour sides for supporting the fluid motors 14 which are in the form ofhydraulic cylinders containing rods 36 which project inwardly therefromat right angles to the sides, there being four such rods. In each endframe 22 (FIG. 1) there are two vertical channel beams 38-38 which bearon the frame at the sides and which, in turn, support vertically spaced,horizontal I-beams 40-40 across which is welded a plate 42. The plates42 support the fluid motors 14 at the end of the furnace with their rods36 extending inwardly into the open ends of the frame. The horizontalbeams 40-40, plates 42 and fluid motors 14 are detachably fastened tothe verticalchannel beams 38-38 and, when detached, are adapted to beraised to the top of the frame by hoists to permit the furnace to beslid into the supporting frame. Each hoist consists of a cable 46attached at one end to an eye fixed in the upper one of the horizontalI-beams and at its other end to a drum 48 on which it is Wound and bymeans of which it may be taken up or let out.

The supporting frame 12 is supported in a horizontal position above thefloor on the piers 16 between the piers 18-18 at the ends and as willappear more fully below such structure makes possible the dumping of theinsulation from the furnace by moving cars under the frame and thenremoving suitable plates at the bottom of the furnace shell provided forthis purpose. The furnace is slid into the supporting frame on theconveyor 19 and, when brought into alignment with the rods 36 of themotors 14, is supported within the supporting frame by means of screwjacks 52 (FIG. 2) which engage against a pair of channel beams 54-54(FIGS. 3 and 4), disposed longitudinally of the furnace 10 at the bottomside thereof.

The furnace comprises an elongate refractory tube 51 (FIGS. 4 and 5),situated within a sheet metal shell 53,

which provides an insulating space about theexterio of the furnace tubewhich is filled with a suitable insulation such as lamp black. Suitablefilling openings may be provided at the top of the shell and dischargeopenings at the bottom of the shell to permit filling and/r removal ofthe insulation. The furnace tube is made up of blocks of graphitedisposed in end-to-end interlocking engagement to form a chamber ofsubstantially rectangular, internal cross-section. In one form thefurnace has a total length of 82 inches and an external cross-section of22" x 22." and an internal cross-section of 12" x 14". The jointsbetween sections are designed to provide space for thermal expansion.The side walls of the tube, internally, have lengthwise thereofsubstantially rectangular recesses 56 of a size about 3" x As shown inFIG. 5, five longitudinal holes 3" in diameter are drilled through thetop and bottom walls of the furnace walls to provide spaces for tengraphite heating rods 60. The holes are drilled larger than the rods andthe rods 60 are held out of contact with the furnace walls by ceramicspacers 62-62 at their ends and may if necessary be spaced therefrom ina well known manner by means of a plurality of small pyrolytic graphitepins engaging with the exterior surface of the rods 64, midway betweenthe ends thereof. The heating rods are made in sections which decreasefrom a maximum at their midsections toward their ends so as to provideprogressively decreasing resistance and hence a desired thermal gradientfrom a maximum temperature at the place of applying pressure in thefurnace, to a lower temperature at their ends. The heating rods may bemade in sections which are fitted together in a conventional mannereither by threading or by slip joints. The outer ends of the heatingrods extend through watercooled copper or aluminum connectors 6666situated at the ends of the furnace tube.

Each end of the furnace tube is connected to the external shell 53 by atube 68 of rectangular, internal crosssection, formed out of one inchgraphite plates. These tubes reduce the end heat losses and provideconvenient support for moving the molds into and out of the furnace.

The furnace tube 51 is supported within the shell 53 and aligned withthe rods of the pressure-applying means by eight cylindrical columns 70,each of which is composed of graphite, insulating zirconia, and steelparts 72, 74 and 76 (FIG. 4). The parts 72 enter the furnace throughsleeves 78 and the parts 74 and 76 are situated within the furnace withthe parts 76 engaged with the wall of the tube. A cap 80 is threaded oneach sleeve 78 and provides means for adjusting the parts; A coil 82 isdisposed about each sleeve 78 and adjacent the outer wall of the shellthrough which a cooling medium may be circulated.

' Substantially midway between the ends of the furnace tube 51 there arefour circular openings 84, one in each wall, in which there is situateda block 86w which is secured to the inner end of a ram 88. The rams 88extend outwardly from the block through the walls of the furnace tubeand the walls of the shell through water-cooled sleeves 90 forengagement through coupling means 95 at their outer ends with the rods36 of the motors 14 supported by the frame 12.

Graphite shells 92 and tubes 94 enclose the blocks 86w and rams 88between the outer surface of the furnace tube, and the shell 53 whichprevent the lamp black thermal insulation from interfering with movementof the moving parts and provide for initial alignment for the rods 36with the rams 88. The blocks 86w and rams 88 may be comprised ofrecrystallized silicon carbide. The blocks 86w at the top and bottomprovide lateral support for the mold and those at the sides provide forapplying pressure for compacting the material contained by the molds.Support for the remaining two sides of the mold is provided through theopen ends of the furnace tube by rams comprised of blocks 86e fixed tothe ends of the rods 36 of the motors 14, supported at each of the endsof the frame,

which have contact with each of the endmost molds of the column of moldssituated in and which fill the furnace tube. The rods 36 and blocks 86ewhich constitute the rams at the ends of the furnace tube, provide, inaddition to lateral support, means for moving the column of moldsthrough the furnace tube. The rods 36 may be driven in a suitablesequence to put pressure on the molds in the column and cause to applypressure to the mold disposed between rams 86w. The rams may also beoperated to release the pressure and effect stepwise feeding of thecolumn of molds.

The use of silicon carbide rams rather than graphite reduces lateralheat loss by six (6) fold, due in part to the greater strength of thesilicon carbide which makes it possible to employ rods 88 of relativelysmall cross-section and inpart to the fact that the silicon carbide alsohas a lower thermal heat conductivity than graphite which wouldotherwise be utilized.

The molds (FIGS. 6 to 9) are hollow open-end boxes 91 of rectangularcross-section, provided at their open ends with plungers 93 movabletoward each other to compact the content of the mold. The moldassemblies 91, 93 are slid into the furnace tube with their open endsdisposed transversely thereof and with the projecting ends of theplungers 93 situated within the recesses 5656, in the side wallsprovided for this purpose. The mold assemblies are moved lengthwise ofthe furnace tube to bring one after another of the molds into the hotzone into alignment with the wall blocks 86w. The top and bottom wallblocks 86w are now brought into engagement with the molds situatedbetween them to support its top and bottom walls and then the end wallblocks 862 at the opposite ends of the furnace tube are brought intoengagement with the endmost molds of the column of molds in the furnacetube to support the side walls of the molds. The mold is thus supportedlaterally at its four sides at right angles to the direction of thecompacting pressure. Compacting pressure is now applied by the wallblocks 86w at the opposite sides. To permit movement of the blocks 86wat the top and bottom sufiiciently to apply the pressure required forsupport, the holes through which the heating rods 60 pass are madesomewhat larger than the rods and may even be made elongated in form ifnecessary, to permit the blocks to move without deflecting the heatingrods and/or breaking the same.

There are two forms of mold box assemblies shown in FIGS. 6 to 9inclusive. The form shown in FIGS. 6 and 7 is made up of fourinterfitted graphite plates 96, each plate being 12 inches wide, 14inches long, and l inch thick, so that the assembled plates provide aninternal opening which is 10" x 10" x 14". The mold in FIGS. 6 and 7 isdivided internally into four cells of equal volume by medially'disclosed partition walls 98 100. The mold shown in FIGS. 8 and 9 ismade up of graphite plates like those used in the mold shown in FIGS. 6and 7, but is provided with a plurality of graphite cores 101 which aredrilled or broached to provide nine (9) longitudinally disposed cells.The plungers 93, which are disposed in the ends of the molds, arecomprised of graphite. If the product or material which is being hotpressed strongly adherent to graphite, thin detachable liners may beemployed. The mold walls are not required to withstand the appliedpressure since the lateral pressure is taken up by the supportsdescribed above. Hence, the walls of the mold may be made much thinnerand hence cheaper than heretofore ever thought possible. i I I Suchdimensions as are referred to herein are solely for the purpose ofillustration and may be changed whenever expedient for the purpose ofmaking the apparatus larger or smaller. Moreover, although the apparatusas described herein was designed for the purpose of hot molding ceramicmaterial, it is to be understood that it may be used for molding anymaterial which requires a high molding temperature which should beapplied to the product while simultaneously subjecting it to asubstantial degree of pressure. V i '7 i l It is to be furtherunderstood that although graphite is referred to as the refractorymaterial used in the construction of the furnace tube, molds and othercertain components of the apparatus, these components may be made ofother suitable refractory material such as aluminum oxide, siliconcarbide, zirconia, titanium diboride, etc. depending upon the particularapplication and the product to be produced therein.

Further, the furnace tube may be heated with gas, fuel oil, orelectrically fired heating apparatus, the choice of which depends onsuch factors as the type of atmosphere desired, and the possiblecontamination of the atmosphere or the product by the combustion gases.

The motion of each ram, the thrust it generates, its sequence of releaseand retraction and the safety devices therefor are controlled at eachstep of the operation by microswitches, electronic pressure-sensitiveswitches and timer controls. Control is effected so that each successivestep must be completed before the next step takes place in the cycle ofoperation.

Referring to FIG. 10, the control means to accomplish these desiderataare shown and the hot pressing process'is initiated with a full columnof mold assemblies in the furnace the center portion of which has beenbrought to the temperature required for the particular molding process,with all of the rams retracted. The rams are as above described drivenby the motors 14 which may comprise cylinders to which a motivatingfluid may be supplied under controlled pressure to advance and retractthe rams. To simplify the description of the sequence of automaticoperation of the rams they will be referred to by the letters R to Rinclusive. Assuming that power is on, the pumps P1, P2 and P3 started, acolumn of molds is situated in the furnace and the timer T has reset andenergized a delay relay DR-Z. To commence the operation, a mold assemblyis placed in the left-hand end of the furnace tube during the delayperiod of a delay relay DR2 and the ram R at the left end of the furnacetube is advanced to the right (FIG. 4) and when relay DR-2 times outenergizing solenoid valve V1, pressure from the pump P1 advances themold column one mold assembly length to the right. The length of theinfeed stroke is determined by a mechanical stop 8-1. This motion tripsa microswitch MS-l which activates a delay relay DR1. During this delaya mold assembly is removed from the right end of the furnace tube. Ifdesired, a mold handling system may be added to push molds into and outof the column. This delay relay DR-l, when it times out, energizessolenoid valve V2 which controls flow of fluid from pump P1 to thecylinder of the motor for ram R at the right end of the furnace tube tomove it into position so that it bears on the right-hand end of thecolumn of molds. This activates a microswitch MS-2 energizing solenoidvalve V3 which supplies a higher pressure from pump P2 to the cylindersof the motors for rams R and R and to the rams R and R so as to bringthe last two named rams into engagement with the top and bottom sides ofthe mold positioned in the hot zone of the furnace to thereby providelateral support for the four sides of the mold perpendicular to thedirection in which the compacting pressure is applied during the hotpressing operation. The actual pressures used to provide the requiredlateral sup port will be determined by experience. In practice, thepressures exerted by the rams R and R will be slightly less than thepressures of the rams R and R which may for this purpose be driven byslightly larger sized pistons than the rams R and R so that the rams Rand R V are held against the stops S-1 and 8-2. The hydraulic pressurein the motors of rams R and R activates two pressure-sensitive switchesPS-l and PS-Z energizing solenoid valves V4 and V5 to supply pressure tothe cylinders of the rams R and R at opposite sides of the mold in thehot zone to thereby apply pressure to the plungers 93 thus to initiatedensification while simultaneously applying heat. The rams R and R areadvanced simultaneously and their movement is controlled bypotentiometers PT-l and PT-Z connected thereto by a rack and pinionmechanism. Their output voltages are opposed and are made to regulateopposed solenoids operatively associated with a valve V6 to balance theaction of the rams. If the ram R advances a distance increment furtherthan the ram R the resultant output is positive and the valve closeswhich supplies pressure to the ram R If the ram R moves an incrementmore than the ram R the resultant voltage is negative and the valvecloses which supplies pressure to the cylinder of the ram R The controlis set so that both valves are open for a small increment of motionbetween these two extremes. This system insures that the loading isapplied symmetrically to prevent torque in the system. After both rams Rand R have advanced a set distance, microswitches MS-3 and MS-4 aretripped energizing solenoid valve V7 providing increased pressure frompump P3 to rams R R R R R and R This pressure activates two pressureswitches PS-3 and PS-4 starting the timer T. The densification processproceeds as before at the higher pressure until the contacts of timer Topen releasing the holding circuit to deenergize all of the hydraulicsolenoid operated valves, to effect the retraction of all the rams bysupplying hydraulic pressure to the opposite ends of all of the ramcylinders so as to withdraw the rams. The delay relays DR'.. and DR-1are reset again when the timer T resets. This ends the cycle. Sixmicroswitches MS-9 to MS-14 inclusive are wired in series with the timercontact to provide for shutting off the hydraulic pressure if any of therams advance beyond a given distance. An accumulator A is provided inthe pressure system.

The temperature of the furnace can be automatically controlled with asuitable means.

It is desirable to have manual controls that by-pass the automaticcontrol system and to provide audio-visual signals to indicate failureof the automatic control system.

Depending on the nature of the material being hot molded, the apparatuscan be cycled in 15 to 30 minutes or for longer or shorter periods. Asingle operator is all that is required for loading and stripping themold and/ or to take care of any difliculties which may be experienced.This is in marked contrast to existing hot molding equipment whichrequires about 2 hours for cycling so that the automatic press disclosedherein has the advantage of approximately ten times the capacity ofprior apparatus.

This apparatus is well adapted to the automatic performance of any wellknown hot pressing process such as is well known in the refractory orceramic arts and powdered metallurgy. Such processing contemplates theapplication of a relatively high degree of pressure to a confined objectwhile the object is subject to a more or less raised temperature toeffect the desired densification and molding of the object. Thepressures required to be used and the temperatures of treatment are wellknown to those skilled in the art and form no part of the presentinvention.

It should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

I claim:

1. The method of hot pressing compressible material comprising,providing a hollow thin wall graphite mold or the like having four sidewalls and open ends, within which is disposed a moldable material,inserting plungers in said open ends to engage said material and extendbeyond the open ends, supporting the mold in the furnace for heating thecontent of the mold up to a predetermined molding temperature and, whilethe mold is in the furnace, applying lateral support to its four wallsperpendicular to the axis through its open ends and applying compactingpressure through the plungers in its open ends to the material thereinin the direction of the axis, said lateral and compacting forces beingapplied from externally of the furmovement through a hot zone in afurnace with their open ends transverse to the direction of movement,applying pressure of equal amount to the endmost molds of the column inopposite directions to support the walls of the mold having contact witheach other against deflection transverse to their open ends, applyingpressure at right angles to the pressure applied lengthwise of thecolumn to the one of the molds intermediate the ends of the column andsituated in the hot zone to support the other two walls of the moldagainst deflection transverse to its open ends, and then applyingpressure to the plungers in the open ends of that mold to compact thematerial in said mold while in said hot zone and while provided withlateral support for its walls.

3. The method of hot pressing compressible material comprising,providing a hollow thin wall refractory mold or the like having fourside walls and open ends, within which is disposed a moldable material,inserting plungers in said open ends to engage said material and extendbeyond the open ends, supporting the mold in the furnace for heating thecontent of the mold up to a predetermined molding temperature and, whilethe mold is in the furnace, applying lateral support to its four wallsperpendicular to the axis through its open ends and applying compactingpressure through the plungers in its open ends to the material thereinin the direction of the axis, said lateral and compacting, forces beingapplied from externally of the furnace without producing reactive forceson the furnace itself. V

4. The method of hot pressing compressible material comprising,providing hollow thin-wall refractory molds or the like having four sidewalls and open .ends, within which is disposed a moldable material,inserting plungers in said open ends to engage said material and extendbeyond the open ends, supporting a column of molds for movement througha hot zone in a furnace with their open ends transverse to the directionof movement, applying pressure of equal amount to the endmost molds ofthe column in opposite directions to support the walls of the moldhaving contact with each other against deflection transverse to theiropen ends, applying pressure, at right angles to the pressure appliedlengthwise of the column to the one of the molds intermediate the endsof the column and situated in the hot zone to support the other twoWalls of the mold against deflection transverse to its open ends, andthen applying pressure to the plungers in the open ends of that mold tocompact the material in said. mold While in said hot zone and whileprovided with lateral support for its walls.

References Cited UNITED STATES PATENTS 3,169,273 2/1965 Brayman.

3,249,964 5/ 1966 Shaler 1816 3,258,514 6/1966 Roach 1816 ROBERT F.WHITE, Primary Examiner.

I. A. FINLAYSON, Assistant Examiner.

1. THE METHOD OF HOT PRESSING COMPRESSIBLE MATERIAL COMPRISING,PROVIDING A HOLLOW THIN WALL GRAPHITE MOLD OR THE LIKE HAVING FOUR SIDEWALLS AND OPEN ENDS, WITHIN WHICH IS DISPOSED A MOLDABLE MATERIAL,INSERTING PLUNGERS IN SAID OPEN ENDS TO ENGAGE SAID MATERIAL AND EXTENDBEYOND THE OPEN ENDS, SUPPORTING THE MOLD IN THE FURNACE FOR HEATING THECONTENT OF THE MOLD UP TO A PREDETERMINED MOLDING TEMPERATURE AND, WHILETHE MOLD IS INTHE FURNACE, APPLYING LATERAL SUPPORT TO ITS FOUR WALLSPERPENDICULAR TO THE AXIS THROUGH ITS OPEN ENDS AND APPLYING COMPACTINGPRESSURE THROUGH THE PLUNGERS IN ITS OPEN ENDS TO THE MATERIAL THEREININ THE DIRECTION OF THE AXIS, SAID LATERAL AND COMPACTING FORCES BEINGAPPLIED FROM EXTERNALLY OF THE FURNACE WITHOUT PRODUCING REACTIVE FORCESON THE FURNACE ITSELF.